Conventionally, there have been disclosed a number of wave pattern classifying methods for the purpose of monitoring the generation of harmful or non-harmful waves.
As the principal approaches for monitoring the state of electro-discharge machining, there are methods such as: analyzing the radio frequency generated during the discharge sparking; measuring and analyzing the electric resistance between the electrode and the object to be machined; and analyzing the discharge wave patterns. Among them, the most preferred was the method of analyzing the wave patterns.
The studies on the analysis of the electro-discharge machining wave patterns which have been carried out so far can be summarized as follows.
That is, the following persons studied on the electro-discharge machining wave patterns: R. Snoeys (CIRP vol 24, 1974), S Bhattacharyya (AASME J. of Eng. Ind., 1980), M. Otto (ISEM7, 1983). A. Endel (ISEM7, 1983), S. Pandit (ASME J. of Eng. Ind., 1984), D. Dauw (CIRP vol 35, 1986,) S. Pandit, ASME J. of Eng. Ind., 1987), and C. Cogun (ASME PED vol 34, 1988).
The contents of the conventional studies are different from the first objective of the present invention in one point. That is, there is a difference in the sampling method. In the conventional studies, there is never found the sampling method of the present invention. In order to clarify this point, the known facts about the discharge wave patterns which occur during an electro-discharge machining operation will be briefly described.
Generally, during a transistorized pulsed electro-discharge machining (to be called "electro-discharge machining" below), 5 types of voltage or current wave patterns (voltage=current x resistance) are generated in a random manner. That is, waves of the normal or effective discharge, arc, short, open and semi-normal discharge are generated (refer to FIG. 1). Of them, only the normal discharge and the semi-normal discharge waves are effective ones. The open wave is not desirable because it lowers the machining efficiency, while the short and arc can damage both the machining apparatus and to the object to be machined, if they continue for a long time. Accordingly, if the 5 wave patterns can be classified at a high speed, it can contribute to monitoring the electro-discharge machining.
The conventional wave pattern classifying method will be described below. There is a difficulty in classifying the 5 types of waves if only the comparison of the voltage levels is used. Therefore, another reference level or another sampling method has to be introduced. In this case, the sampling is carried out by distinguishing the discharge pattern into an initial period and a final period.
Conventionally, a number of methods have been disclosed for the purpose of monitoring the generation of harmful arcs. The discrimination as to whether there are arcs is made based on the increase of the average current or the drop of the voltage across the discharge electrode, thereby preparing for future measures against the generation of arcs. For example, measures such as causing an off-time and the like are taken, with the result that effective results are gained.
However, such a conventional method is different from a second object of the present invention in two points. That is, a discrimination is carried out for every discharge pulse, and then a proper measure is taken before the completion of the individual pulse. In other words, the measurement, classification and adjustment are almost simultaneously carried out for every pulse.